This invention relates to a process for the production of a finely divided crystal suspension in which a melt is mixed with, and emulsified in, a colder aqueous phase at a temperature below the crystallization point of the molten material, the melt solidifying in the form of the dispersed particles only after the emulsification step.
Melts are normally dispersed by initially dispersing the melt above its solidification temperature in an aqueous phase, followed by cooling to below the crystallization temperature of the organic phase. Cooling may take place in a stirred tank, by heat exchangers or by the water phase itself (cf, for example EP-A-221 465). The disadvantage of this process is that relatively large crystals grow from the dispersed particles. It is also known that a melt can be dispersed in an aqueous phase having a temperature below the solidification temperature of the melt. According to DE-PS 2 551 841 and 29 00 268 for example, dispersions of this type are produced using high-speed stirrers or rotor-stator machines. The disadvantage of these processes is that they only give coarse dispersions with short shelf life. The formation of stable dispersions requires either stirred storage tanks (DE-PS 2 900 268), the addition of thickeners or an additional homogenization step (DE-PS 2 551 841), for example in stirred ball mills.
The problem addressed by the present invention was further to develop and improve the emulsion crystallization process described above in such a way that very finely divided crystal suspensions of spherical particles (particle diameter .ltoreq..mu.m) can be economically produced at high throughputs.